[Mesa-dev] [PATCH] i965: Only emit interpolation setup if there are actual FS inputs.

[Eric Anholt]

Kenneth Graunke <kenneth at whitecape.org> writes:

> Dead code elimination would get rid of the extra instructions, but
> skipping this saves iterations through the optimization loop.
>
> From shader-db:
>
>       N     Min     Max        Median           Avg        Stddev
> x 14672       3      16             3     3.1334515    0.59904168
> + 14672       1      16             3     2.8955153    0.77732963
> Difference at 95.0% confidence
>         -0.237936 +/- 0.0158798
>         -7.59342% +/- 0.506783%
>         (Student's t, pooled s = 0.693935)
>
> Embarassingly, the classic shadow mapping shader:
>
>    void main() { }
>
> used to require three iterations through the optimization loop.
> With this patch, it only requires one (which makes no progress).

Reviewed-by: Eric Anholt <eric at anholt.net>
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